M.K.
Your doctor is probably being overly cautious because hypertonicity in infants is linked to neurological problems. One of these problems, hyperekplexia, can cause SIDS if left untreated. I haven't been in this situation, but from the little I know it might be worth getting the EEG just to be safe. They won't be injecting your child with chemicals or anything; they just put sensors on to measure brain activity and there aren't any side effects. The hard part will be keeping a six-month-old awake from 5-10am...